The instant invention relates to apparatus for driving paper webs having tractor holes, and more particularly to auxiliary drive apparatus for webs having tractor holes on only one side of the web.
Many paper handling systems, such as envelope inserting systems, employ paper webs which are ultimately severed into discrete sheets. Typically, the paper web includes tractor holes on both longitudinal margins which are engaged by the pins of a tractor drive. As web handling applications have become increasingly complex, there has developed a need for the capability to process paper webs having tractor holes on only one side, e.g. "center-slit" and "two-up" applications.
With a single side tractor drive scheme, the paper forces, such as acceleration and deceleration, have a tendency to skew the paper web as the web is processed at high speeds, thereby yielding unacceptable cut and slit geometries and high jam frequencies. Since all paper webs eventually must be cut or severed in some way into discrete sheets, and because traditional severing and transport mechanisms do not function well when driving a web by only one set of tractor holes, an enhanced drive scheme is required to enable a web with only a single set of tractor holes to be processed at the high speeds, accelerations and decelerations associated with "state-of-the-art" performance.
There have been many attempts to provide such an enhanced drive scheme for webs with one set of tractor holes. Most frequently, a friction roller and associated idler roller are fashioned to drive the non-tractor driven edge of the web. The roller is driven by the spline that typically drives the tractor assemblies. Unfortunately, it is virtually impossible to consistently maintain the necessary part geometries (roller diameter) to have the friction roller system work in concert with the associated tractor on the other side of the web. If the roller varies by even +/-0.001", every revolution of the roller will yield a tolerance build-up of 0.003 inch. After 20 revolutions, the cumulative error will be approximately 0.060". The additive nature of this tolerance build-up quickly results in jam conditions. Some of the attempts have incorporated the opportunity for the roller to slip and relieve this tolerance build-up, but this adaptation yields poor paper handling characteristics and has an extremely sensitive system set-up. These problems are compounded as the paper characteristics (weight, thickness, surface finish, etc.) are varied.
Accordingly, the instant invention provides an auxiliary drive to the non-tractor driven edge of a paper web so that a transport force can be applied to that edge of the web without the need for tractor holes. The auxiliary drive of the instant invention applies positive web transport forces to the non-tractor driven side of the paper web while allowing tolerance build-up between the auxiliary drive and the tractor drive to be easily and quickly dissipated.